Multiplex receiver system



jTI'OSS Reference E Oct. 16, 1934. E} v. AMY ETAL 1,976,909 I MULTIPLEPXREbEIVER SYSTEII Filed April 24, 1929 2 Sheets-Sheet l FIG. 1 RECEIVERREC.

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INVENTOR M I ATTORNEY Examinel Cross HgEi-arence E. v. AMY ET ALMULTIPLEX RECEIVER SYSTEM Oct. 16, 1934.

2 Sheets-Sheet 2 Filed April 24, 1929 FIG. 5

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' INVENTOR ERNEST v. AMY AND BY JULIUS amzvzs \ATTORNEY aUNlTEDsTATEsPATENT OFFICE I MoLrrPLEx RECEIVER SYSTEM Ernest V. Amy and JuliusG. Aceves, New York,

1. York N. Y., assignors to Amy, Aceves & King, Incorpcrated, New York,N. Y., a corporation of New e Application'April 24, 1929, Serial No.357,652

, This invention relates to a multiplex high frequency receiving systemfor operating a plurality of high frequency receivers from the samepickup device with minimized interference or in- 1;. ter-action betweensaid receivers, and is particularly applicable to simultaneous operationof a number of radio receivers operating from the same antenna, as, forexample, in the ease of an apartment house or hotel, where a singleantenna .10 is provided to which a number of radio receivers areconnected.

, Heretofore, in cases where it is desired to operate a considerablenumber of receivers in the same building, as for example, in the case ofapart- 11 ment houses, hotels and the like, in which there {3- ber ofaerials by individuals, each one of whom are or may be a considerablenumber of radio receivers, it has been customary for each operator toprovide his own antenna and lead-in system connected to his receiver.The antennas are usu- 'Ifg ally erected upon the roof of the building,and

usually this results in the erection of a consid- Ierable number ofaerials in adjacent positions in which the coupling between the aerialsis so great that the operation of any receiving set Can- .5 2 nected toone aerial is materially affected bythe operation of another setconnected to an adjacent aerial.

In addition to interference between receivers soconnected and operated,the erection of a nummay have different ideas" of construction,disfigures the building and may even result in property damage to thebuilding and actual danger to the tenants if, for example, the aerialsare not properly grounded and protected against lightning.

It is an object of this invention to provide a system whereby a numberof receivers may be operated from the same antenna.

.- I It is a further object of this invention to provide a systemwhereby a number of receivers may be operated from the same antenna andmay be tuned to different frequencies, the system being so arranged thata variation of tuning of one receiver will not change the signal voltagefed tenna by a greater percentage than if the second receiver wereoperated on its own aerial under 7 in which each of the receiversconnected tothe antenna is fed with a signal having a strength .55 asgood rbetterthan the receiver would obtain 2 Claims. (01. 250-9) toanother receiver connected tothe same anif it were fed by its ownantenna under the conditions hereinbefore described. f, .It is a furtherobject of this invention to provide a system of the class described, inwhich the lead-in conductor may pass from floor to floor or may pass toa plurality of receivers located on the same floor without introducingundesirable effects from one receiver to another, as already pointedout.

It is a further object of this invention to provide 4 a system of theclass described, in which the leadin conductor acts as a uniformattenuation line passing all frequencies of the band desired to bereceived by any receiver connected thereto, and which is so arranged asto prevent the production 21 0 of standing electrical waves upon thelead-in conductor.

It is a further object of this invention to provide a system of theclass described which may be so arranged as to reduce the strength ofsig- 2 :5 nals of any particular frequency fed to the associatedreceivers.

1 will best be understood by reference to the sped-.

fication and accompanying drawings, in which like reference numeralsindicate like elements,

-and in which: 1

ing the preferred method of coupling a single receiver to thetransmission line or lead-in con- Figure 3 shows, diagrammatically, amodifiedarrangement according to our invention, and

Figures! and 5 show still further modified forms of our invention.

In its fundamental aspect our invention comprises a pickup device suchas an antenna, which may, for example, be mounted upon the roof of thebuilding, provided with a lead-in conductor passing from floor to floorand, if desired, to a plurality of locations upon one or more floors..-,A

number of radio receivers are coupled to said'iIO The intermediateloading coils preferably all have substantially equal inductance, whilethe initial and final loading coils preferably have'an inductance equalto one-half that of the inter mediate loading coils.

For the purpose of preventing standing waves on the transmission line,the end of the line or lead-in is preferably connected to ground througha resistance equal to the terminal or surge impedance of the line, thatis While we do not desire to limit ourselves to particuiar constants, wehave found that very satisfactory results are obtained in broadcastreceivers when the intermediate loading coils have inductances ofmicro-henrys, the initial and final loading coils inductances of 40micro-henrys, and the coupling condensers for the various receivers havecapacities of 250 m. m. f., and the terminal resistance has a value of400 ohms. Under such conditions the transmission line will passfrequencies as high as 1600 kilocycles, approximately.

Referring now more particularly to Fig. 1: 1 designates the antenna orpickup; 2 the lead-in conductor; -3 and 6 the initial and terminalloading coils, and 4 and 5 the intermediate loading coils. The lead-inconductor 2 is grounded through resistance 7, equal to the surgeimpedance of the line, and the various receivers 9, 11 and 13 areconnected at their ground terminal to a suitable ground such as theradiator pipe 14 extending through the building, which in turn isgrounded as at 15. The antenna terminal of the various rece'vers isconnected through condensers 8, 10

1 and 12, respectively, to-points intermediate the loading coils 34, 45and 56, respectively.

The insertion of the radio receiver in series with the couplingcondenser will change the value both of the resistance and the reactanceof the line at that point, but it is desirable that this change bemadeso small that the effect on the other receivers will not be greaterthan-the inter-action which would obtain between such receivers if theywere eachconnected to their own antenna mounted upon the roof under theconditions heretofore usual. If the impedance of the receiver isapproximately 1000 ohms, the revoltage which issuppliedto the receiver.In general; it-r'nay be'stated that the best values actence of thecondenser coupling the receiver to the lead-in conductor should be ofthe same order of magnitude. Condensers of smalier capacity and loadingcoils of larger inductance may be used if it is desired to reduce stillfurther the action 'of one receiver on ancther, but it will beunderstood that this will tend to decrease the signal of inductance andcapacity for any particular In installing the lead-in conductor, it ispreferable, although not necessary, to install it as shown more indetail in Fig. 2, wherein 18 indicates, diagrammatically, the N floor ofthe building, and 19 the (N+1) floor. The lead-in conductor 2 ispreferably cut at each floor and se- 80 cured in position by means of aninsulator 16. The loading coil here indicated as 4 is connected tobridge the gap in conductor 2, formed by the insertion of the insulator16. The receiver 9 has its ground terminal connected to ground, as for35 example on the radiator pipe or water pipe, and its antenna terminalconnected to one side of condenser 8, the other side of which isconnected to the lead-in conductor 2 and the top end of loading coil 4.I

It will be understood that while we have shown a definite number ofreceivers in the drawings, this is merely by way of example and that thenumber of receivers connected may be varied.

In the various figures the same reference characters have been used toindicate similar elements, but it will be understood that the constantsof such elements will be chosen under any particular condition so as togive the best results.

Referring now more particularly to Fig. 3, we have indicateddiagrammatically a system wherein a number of receivers upon the samefloor, as well as receivers upon different floors, are 0perated from thesame antenna. In this figure (N+1), (N+2) and N+3 represent the variousfloors, and it will be noted that on the N floor, receivers 13, 25 and27 are operated connected to the lead-in 2 by means of condensers 12, 24and 26, respectively, and separated by loading coils 20 and 21,respectively.

Referring now more particularly to Fig. 4, we have shown an arrangementwhich may be utilized when it is desired .to reduce the voltage of anyparticular frequency fed to the various receivers for any reason, forexample if the antenna is located in the vicinity of a powerfultransmitter. In this arrangement a trap circuit, consisting for exampleof inductance 30 and condenser 31 in parallel therewith, may be insertedin series in thelead-in 2 and tuned to the frequency of the signal whichit is desired to reduce. In addition, other trap circuits may beinserted at other points if desired; for example, the trap circuit shownas condenser 32 and inductance 33 connected in series may be connectedfrom the lead-in 2 to ground and tuned to the frequency of the signalwhich it is desired to reduce.

It may also be desired to increase the strength of a signal of aparticular frequency, and this. may be done as shown by way of examplein Fig." 5. The lead-in conductor 2 may be connected at an intermediatepoint on inductance 35, which thus constitutes an auto-transformer andis tuned, forexample, by means of condenser 36. One terminal ofinductance 35 may be cc-nnected to the grid of an ordinary vacuum tubeamplifier 38, while the other terminal of inductance 35 is connected toone end of variable resistance 37, the other terminal of which isconnected te o ground and to the'filament of amplifier-38. The operatingpotential for the plate circuit of amplifier 38 may be supplied by asuitable source of potential 40, preferably connected in series withinductance 39. A tuned circuit, for example in -11 ductance 41, inseries with condenser 42, is connected to the commontermin'al of theplaten! amplifier 38 and inductance 39 and to the trans mision line 2,and a variable resistance 43'n'1ay be connected between this point andnoun-$15 By tuning the circuit 35 and 36 to the frequency which it isdesired to increase, and by properly choosing the values of inductance35, condenser 36 and resistance 37, and also by varying the position ofthe tap upon inductance 35, the voltage available on the grid circuit ofamplifier 38 is made greater for signals of the frequency which it isdesired to increase than for other frequencies, since it will beunderstood that the potential difference across resistance 37 isimpressed across the input of amplifier 38 at all frequencies, whereasvoltages of the frequency to which condenser 36 and inductance 35 aretuned are effective only at frequencies at or near resonance. Byproperly choosing the values of the various variables, such asinductance 35,'condenser 36, resistance 37, and also inductance 41,condenser 42, the desired curve of selectivity may be obtained. Morespecifically, in the plate circuit the value of inductance 41 andcondenser 42 may be controlled with respect to the plate resistance ofthe tube to give the desired steepness to the selectivity curve.

In this case also we have indicated variable resistance 43 connectedbetween the transmission line and ground. This should be of a valueclose to the terminal impedance of the transmission for best results.

It will be understood that the antenna itself has certain values ofinductance capacity and resistance, and that under certain conditionsthese may not be the optimum value desired from a theoreticalstandpoint. Therefore, under certain conditions it may be founddesirable to provide a compensating network at the beginning of thetransmission line or lead-in conductor 2 for the purpose of matching theantenna and line. However, we find that under most conditions this isnot essential and may be omitted.

It will be understood that'in accordance with our invention a number ofradio receivers may be supplied from the same antenna, regardless ofwhether these receivers are located on the same floor or on diiferentfloors, or whether a plurality of receivers are located on each floor.It will also be understood that our invention is not limited to anyparticular type of condenser or loading coil, and, if desired, theloading coil may be formed by winding the desired number of turnsdirectly upon the insulator which secures the adjacent ends of thelead-in conductor.

While we have shown and described certain preferred embodiments of ourinvention, it will be understood that modifications and changes may bemade without departing from the spirit and scope of our invention, aswill be understood by those skilled in the art.

We claim:-

1. In a multiplex high frequency receiving system for operating aplurality of receivers from the same antenna, a line conductor connectedto said antenna, a plurality of effectively grounded radio receiversconnected through a coupling impedance to said line conductor, andloading coils interposed in said line conductor between said antenna andthe first receiver, between said receivers and between the last receiverand ground,

the inductance of all of said loading coils, except the first and last,being substantially equal, and the inductance of said first and lastloading coils being substantially equal to one-half the inductancebetween said receivers.

2. A multiplex high frequency receiving system for operating a pluralityof receivers from the same antenna, comprising, in combination, anantenna, a ground, a line conductor connected between said antenna andground through a terminating impedance, a plurality of radio receiversconnected between said line conductor and ground, loading coilsinterposed in said line conductor between said receivers, and meansassociated with said system for selectively changing the relationbetween the amount of energy of a predetermined frequency absorbed bysaid antenna and delivered to said receivers.

ERNEST V. AMY JULIUS G. ACEVES.

